Connected: An Internet Encyclopedia
RFC 1123 - 4.1.3.3 Concurrency of Data and Control

Top: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1123
Up: 4. FILE TRANSFER
Up: 4.1 FILE TRANSFER PROTOCOL -- FTP
Up: 4.1.3 SPECIFIC ISSUES
Prev: 4.1.3.2 Idle Timeout
Next: 4.1.3.4 FTP Restart Mechanism

### 4.1.3.3 Concurrency of Data and Control

DISCUSSION:

  The intent of the designers of FTP was that a user should be able to send a STAT command at any time while data transfer was in progress and that the server-FTP would reply immediately with status -- e.g., the number of bytes transferred so far. Similarly, an ABOR command should be possible at any time during a data transfer.

  Unfortunately, some small-machine operating systems make such concurrent programming difficult, and some other implementers seek minimal solutions, so some FTP implementations do not allow concurrent use of the data and control connections. Even such a minimal server must be prepared to accept and defer a STAT or ABOR command that arrives during data transfer.

Next: 4.1.3.4 FTP Restart Mechanism

Connected: An Internet Encyclopedia
RFC 1123 - 4.1.3.3 Concurrency of Data and Control